1. Field of the Invention
This invention relates to a lighting device which is used to illuminate during military blackout applications and also in conjunction with night vision goggles. The preferred embodiment relates to a flashlight, however, the invention is not limited to that use as it will also find application in permanently mounted fixtures and with power sources other than batteries.
2. Related Art
For the past 40 years, the military has employed red light in those instances when blackout security was required Blackout situations required personnel to substantially reduce their detectability while still permitting them to carry out their assigned tasks Some of these assigned tasks such as the reading of colored maps, required color discrimination while others such as piloting aircraft required extremely sensitive eyesight It was known that the use of red light created problems in color discrimination. However, this defect was accepted because the red light did not substantially impair the ability of the soldiers to detect low levels of light, i.e., the red color did not reduce the peripheral retinal sensitivity of the eye.
During the past ten years the military has been developing and using night vision goggles. These goggles permit users to see in the dark by amplifying the incoming radiation in the visible and near infrared range up to 40,000 times. As these goggles became more widely used, it was found that the red lighting system in use was not compatible with the goggles. The red light prevented the goggles from functioning properly by overwhelming them with ambient red and infrared energy.
Many of the military applications are now using a blue/green color, Anvis Green A, for their blackout lighting operations. The ANVIS GREEN colors are defined in Military Specification, MIL-L-85762, LIGHTING, AIRCRAFT, INTERIOR, AN/ANV-6 AVIATOR'S NIGHT VISION IMAGING SYSTEM (ANVIS) COMPATIBLE, 24 Jan. 1986. The switch to the new blue/green color was made only after extensive testing showed that this color would, like the red, have minimal effect on the peripheral retinal sensitivity of the eye and simultaneously it would not interfere with the use of night vision goggles.
However, for blackout conditions the blue/green color has the same defect as the red color in that it fails to accurately reveal for the user the full range of colors that may be found on military maps or as are present in the military work place.
The concept that blackout lighting had to be colored has been a long established military concept which is still in use today. There are numerous pieces of military equipment which are in use based upon the concept that color lighting was necessary for blackout situations. One such piece of equipment is a portable lighting device described in U.S. Pat. No. 4,517,628, which permits the color to be changed from incandescent white to red for blackout conditions. Therefore, prior art and long established convention both dictate that unfiltered incandescent white light cannot be successfully used for illumination under blackout conditions. Portions of this invention use prior art U.S. Pat. No. 4,677,533, which relates to a lighting device intended for color discrimination but not designed for blackout lighting or use near night vision goggles.